The ruins of Fountains Abbey. The National Trust has advertised for a visitor experience development intern for this property.
Photograph: The National Trust Photolibrary/Alamy

The National Trust has been accused of using dozens of unpaid interns to complete the work of full-time administrative roles at its properties and head office.

The charity, which currently has 33 unpaid workers in placements that last for six months, has been accused by employment campaigners of using rolling adverts for internships with paid travel and lunch expenses to boost its workforce.

The trust is advertising on its website for a visitor experience development intern (pdf) for its Fountains Abbey and Studley Royal property, a position that has a suggested time commitment of three days, or 22.5 hours, a week for six months.

“You’ll be working on a number of projects and also be involved in the day-to-day organisation and running of the department. There is also the potential to become involved with other teams to support your own career interests,” the advertisement reads.

Anyone who qualifies as a worker, with set hours and responsibilities and doing work that would otherwise need to be done by a paid member of staff, must be paid at least the minimum wage if under 25, or the national living wage if 25 or over.

However, some charities are using an exemption intended to protect the concept of volunteering to avoid paying interns.

Tanya de Grunwald, campaigner for fair internships and founder of careers blog Graduate Fog, said the entire charity sector was “way behind the times” on internships.

“Clearly it is not reasonable to ask someone to work unpaid for months on end. Other members of staff don’t work for free – this logic is only applied for junior workers,” she told the Guardian. “What disturbs me the most is when charity interns tell me they have explained to their line manager how difficult it is to work for free, the boss says, ‘We’re a charity’, and the intern comes away feeling they have been unreasonable in asking for a wage for the job they are doing.

In November London zoo was criticised for seeking a master’s degree graduate to help run a global conservation project for no payment other than £5 a day for lunch and a Travelcard.

A National Trust spokesperson said it had 61,000 volunteers, of which just 33 were interns.

“All internships support projects, rather than everyday business, and placements last no longer than six months. While the Trust cannot guarantee an internship will lead to paid employment, a good number of our previous interns have found employment with us and many more have gone on to find jobs in related sectors.”